Various electro-optical systems have been developed for reading optical indicia, such as barcodes. A barcode is a coded pattern of graphical indicia comprised of a series of bars and spaces of varying widths, the bars and spaces having differing light reflecting characteristics. The pattern of the bars and spaces encode information. Barcodes may be one dimensional (e.g., UPC barcode) or two dimensional (e.g., DataMatrix barcode). Systems that read, that is, image and decode barcodes employing imaging camera systems are typically referred to as imaging-based readers or scanners.
Imaging-based readers may be portable or stationary. A portable reader is one that is adapted to be held in a user's hand and moved with respect to target indicia, such as a target barcode to be read, that is, imaged and decoded. Stationary readers are mounted in a fixed position, for example, relative to a point-of-sales counter. Target objects, e.g., a product package that includes a target barcode are presented or swiped past one or more transparent windows and thereby pass within a field-of-view of the stationary readers.
The imaging based readers typically comprise a sensor or photodetector that collects light reflected from the target indicia located on an article or target object. The sensor or photodetector typically comprise charge coupled device (CCD) arrays, complementary metal oxide semiconductor (CMOS) arrays, or other imaging pixel arrays having a plurality of photosensitive elements or pixels.
A corresponding analog signal is generated by the sensors that are decoded into a digital signal representative of the target indicia being read. In general, the photosensors discussed above in areas of inadequate ambient lighting require a source of illumination that is scattered across the target indicia within or over the photosensor's field-of-view in order to produce the analog signal. A typical illumination system comprises light emitting diodes (LEDs), cold cathode florescent lamps (CCFLs), and the like that act as an illumination source for the imaging reader.